Federal lawmakers are taking a harder look at whether politics drove a decision by the Federal Aviation Administration to approve Cape Wind.

In a joint letter sent Tuesday to FAA acting administrator Michael Huerta, the Republican chairmen of two House committees reiterated concerns about references to the highly political nature of the proposed Nantucket Sound wind farm raised in internal agency emails and other documents.

"It would be most troubling if FAA officials felt political pressure to approve the Cape Wind project despite both internal and external concerns over its safety, and even more so if the FAA disregarded these safety concerns and made its decision because, as one manager stated, 'It would be very difficult politically to refuse approval of the project,'" U.S. Rep. Darrell Issa, R-Calif., chairman of the Committee on Oversight and Government Reform, and U.S. Rep. John Mica, R-Fla., chairman of the Committee on Transportation and Infrastructure, wrote in the four-page letter.

"A politically based determination of the Cape Wind project by the FAA is an unacceptable use of federal authority, contravenes FAA's statutory mandate, and raises significant safety concerns for aviation in Nantucket Sound," they wrote.

In their letter, Issa and Mica asked for a series of documents related to the FAA decision on Cape Wind and specifically whether political considerations entered into the decision.

"Did the administration's promotion of green energy production factor into FAA's decision and if so, in what way?" the men asked in one multi-part question.

The powerful GOP lawmakers asked that the documents and answers to their questions be delivered by July 31.

President Barack Obama's Interior secretary, Kenneth Salazar, approved the Cape Wind project in April 2010. The FAA signed off on the project in May 2010.

However, in October 2011 a federal judge sent the decision — the 440-foot-tall turbines posed no hazard to air navigation — back to the agency for more review.

The FAA has yet to issue a new finding for the project.

Questions about political influence on the FAA's approval gained steam in June after Cape Wind opponents secured emails and other documents from the agency through a Freedom of Information Act public records request.

"It continues to show a clear pattern of politics over public safety," said Audra Parker, president and chief executive officer of the primary anti-Cape Wind group, the Alliance to Protect Nantucket Sound.

Regardless of political party, presidential administrations and congressional leaders should be putting public safety ahead of a green energy agenda, Parker said.

"We've won a court case, and now there's a congressional probe," Parker said. "It's public safety over politics."

Cape Wind's supporters, including the major environmental organizations Greenpeace, Oceana and the Conservation Law Foundation, moved quickly to defend the project.

"What we're seeing here is a series of these folks in Congress carrying water on behalf of the Cape Wind opponents," said Seth Kaplan, vice president for policy and climate advocacy at the Conservation Law Foundation. "This is nothing but a transparent delay tactic seeking to slow down what is probably the most reviewed energy project in the history of the country."

Comments by FAA officials about the political nature of Cape Wind is simply contextual fact, Kaplan said.

"Perhaps they also commented that it was hot outside or that the sky is blue," he said.

An FAA spokesman did not respond to questions about the letter.

In a statement emailed to the Times, Cape Wind spokesman Mark Rodgers wrote the only political pressure regarding the project has come from opponents.

"On air navigation safety, the FAA has been carefully reviewing Cape Wind for 10 years and has approved it three times, twice during the Bush administration and once under the current administration, despite pressure from a well-funded opposition group," Rodgers wrote. "We are hopeful that the extensive, ongoing FAA review will reach the same conclusion: Cape Wind will not be hazardous to air navigation — just as Europe's 40 offshore wind farms built over the past 20 years have not posed any problems for safe air navigation there."

It is too early to say if the investigation would lead to hearings, according to Issa spokesman Jeffrey Solsby.

"At this point, it's a matter of letting the letter be received and seeing answers to the questions," Solsby said.

After Cape Wind's opponents called for an investigation by the U.S. Department of Transportation's Office of Inspector General into whether political pressure affected the FAA's approval, U.S. Rep. Clifford Stearns, R-Fla., who spearheaded a probe into a $535 million federal loan for the now-bankrupt solar company Solyndra, agreed such an investigation was warranted.

Since then, other lawmakers have called for a similar investigation, including U.S. Sen. Scott Brown, R-Mass.

The FAA approval is the final remaining permitting hurdle for Cape Wind.

A group of Martha's Vineyard fishermen recently settled a lawsuit against the federal government about its approval of the project, but a series of other legal challenges to that approval are still pending in federal court.